U.S. patent number 7,109,512 [Application Number 10/924,395] was granted by the patent office on 2006-09-19 for optical transducer for detecting liquid level and electrical circuit therefor.
This patent grant is currently assigned to Opti Sensor Systems, LLC. Invention is credited to Alvin R. Wirthlin.
United States Patent |
7,109,512 |
Wirthlin |
September 19, 2006 |
Optical transducer for detecting liquid level and electrical
circuit therefor
Abstract
An optical transducer for determining the presence or absence of
liquid or the like in a reservoir includes an electrical circuit
with a pulse generator and processing electronics to filter out
ambient light and compensate for temperature changes. A comparator
circuit portion includes a pair of comparators that simultaneously
output high and low signals when in the presence of liquid. One of
the outputs can be selected to drive an indicator, pump, relay or
the like.
Inventors: |
Wirthlin; Alvin R. (Lucas,
TX) |
Assignee: |
Opti Sensor Systems, LLC
(Lancaster, VA)
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Family
ID: |
35242288 |
Appl.
No.: |
10/924,395 |
Filed: |
August 23, 2004 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20050236592 A1 |
Oct 27, 2005 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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10829772 |
Apr 22, 2004 |
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Current U.S.
Class: |
250/573;
250/227.11; 356/627 |
Current CPC
Class: |
G01F
23/2922 (20130101); G01F 23/2925 (20130101) |
Current International
Class: |
G01N
15/06 (20060101); G01N 21/49 (20060101); G01N
21/85 (20060101) |
Field of
Search: |
;250/227.11,573,577
;356/627 ;385/12-13 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Epps; Georgia
Assistant Examiner: Lee; Patrick J.
Attorney, Agent or Firm: Wirthlin; Alvin R.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a Continuation-in-Part of U.S. application Ser.
No. 10/829,772 filed on Apr. 22, 2004.
Claims
I claim:
1. A liquid level transducer, having a transparent body adapted for
exposure to a liquid to be measured, the liquid level transducer
comprising: an electrical circuit comprising: a light source for
projecting radiant energy into the transparent body; a photosensor
for detecting a level of the radiant energy emanating from the
transparent body, the level of radiant energy being indicative of
the presence or absence of liquid on the transparent body; a
pulsing circuit portion connected to the light source for pulsing
the light source between on and off conditions; a rectifier circuit
portion connected to the photosensor for rectifying a signal from
the photosensor, the rectified signal being proportional to the
detected level of radiant energy; an integrator circuit portion
connected to the rectifier circuit portion for temporarily storing
the rectified signal; a comparator circuit portion connected to the
integrator circuit portion for comparing the rectified signal with
a predetermined value; and a load switch portion connected to the
comparator circuit portion for switching an external load when the
rectified signal is at least one of above and below the
predetermined value; wherein the comparator circuit portion
comprises first and second comparators, the first comparator being
configured to output a high signal to the load switch portion when
the rectified signal is above the predetermined value, the second
comparator being configured to output a low signal to the load
switch portion when the rectified signal is above the predetermined
value.
2. A liquid level transducer according to claim 1, and further
comprising a selector switch portion connected between the outputs
of the first and second comparators and the load switch portion for
selecting the output of only one of the comparators.
3. A liquid level transducer according to claim 1, and further
comprising an anti-hysteresis circuit portion connected to the
inputs and outputs of the comparators to prevent oscillation of the
load switch portion.
4. A liquid level transducer, having a transparent body adapted for
exposure to a liquid to be measured, the liquid level transducer
comprising: an electrical circuit comprising: a source for
projecting radiant into the transparent body; a photosensor for
detecting a level of the radiant energy emanating from the
transparent body, the level of radiant energy being indicative of
the presence or absence of liquid on the transparent body; a
pulsing circuit portion connected to the light source for pulsing
the light source between on and off conditions; a rectifier circuit
portion connected to the photosensor for rectifying a signal from
the photosensor, the rectified signal being proportional to the
detected level of radiant energy; an integrator circuit portion
connected to the rectifier circuit for temporarily storing the
rectified signal; a comparator circuit portion connected to the
integrator circuit portion for comparing the rectified signal with
a predetermined value; a load switch portion connected to the
comparator circuit portion for switching an external load when the
rectified signal is at least one of above and below the
predetermined value; and a delay timer connected between the
integrator circuit portion and the comparator circuit portion to
thereby prevent or reduce false signaling due to liquid
sloshing.
5. A liquid level transducer according to claim 4, wherein the
integrator circuit portion comprises a first resistor in series
with a capacitor and the delay timer comprises a second resistor in
parallel with the capacitor.
6. An electrical circuit for a liquid level transducer having a
transparent body adapted for exposure to a liquid to be measured,
the electrical circuit comprising: a light source adapted for
projecting radiant energy into the transparent body; a photosensor
adapted for detecting a level of the radiant energy emanating from
the transparent body, the level of radiant energy being indicative
of the presence or absence of liquid on the transparent body; a
comparator circuit portion connected to the photosensor for
comparing the detected level of radiant energy with a predetermined
value, the comparator circuit portion comprising first and second
comparators, the first comparator being configured to output a high
signal when the detected level of radiant energy is above the
predetermined value, the second comparator being configured to
output a low signal when the detected level of radiant energy is
above the predetermined value; and a load switch portion connected
to an output of at least one of the first and second comparators
for switching an external load when the detected level of radiant
energy is at least one of above and below the predetermined
value.
7. An electrical circuit according to claim 6, and further
comprising a selector switch portion connected between the outputs
of the first and second comparators and the load switch portion for
selecting the output of only one of the comparators.
8. An electrical circuit according to claim 7, and further
comprising an anti-hysteresis circuit portion connected to the
inputs and outputs of the comparators to prevent oscillation of the
load switch portion.
9. An electrical circuit according to claim 6, and further
comprising an anti-hysteresis circuit portion connected to the
inputs and outputs of the comparators to prevent oscillation of the
load switch portion.
10. An optical transducer for determining the presence or absence
of liquid in a reservoir, the optical transducer comprising: a
housing having a hollow interior; an optical probe extending
through the housing, the optical probe having a proximal end
positioned in the hollow interior and a distal end positioned
outside of the housing; electrical circuitry for determining the
presence or absence of liquid on the distal end of the optical
probe, the electrical circuitry comprising: a light source
positioned for projecting radiant energy into the optical probe
toward the distal end; a photosensor positioned for detecting a
level of radiant energy reflected from the distal end, the level of
radiant energy being indicative of the presence or absence of
liquid on the optical probe; a comparator circuit portion connected
to the photosensor for comparing the detected level of radiant
energy with a predetermined value, the comparator circuit portion
comprising first and second comparators, the first comparator being
configured to output a high signal when the detected level of
radiant energy is above the predetermined value, the second
comparator being configured to output a low signal when the
detected level of radiant energy is above the predetermined value;
and a load switch portion connected to an output of at least one of
the first and second comparators for switching an external load
when the detected level of radiant energy is at least one of above
and below the predetermined value.
11. An optical transducer according to claim 10, and further
comprising a selector switch portion connected between the outputs
of the first and second comparators and the load switch portion for
selecting the output of only one of the comparators.
12. An optical transducer according to claim 11, and further
comprising an anti-hysteresis circuit portion connected to the
inputs and outputs of the comparators to prevent oscillation of the
load switch portion.
13. An optical transducer according to claim 10, and further
comprising an anti-hysteresis circuit portion connected to the
inputs and outputs of the comparators to prevent oscillation of the
load switch portion.
14. An optical transducer according to claim 10, and further
comprising: a pulsing circuit portion connected to the light source
for pulsing the light source between on and off conditions; a
rectifier circuit portion connected to the photosensor for
rectifying a signal from the photosensor, the rectified signal
being proportional to the detected level of radiant energy; and an
integrator circuit portion connected between the rectifier circuit
portion and the comparator circuit portion for temporarily storing
the rectified signal.
15. An electrical circuit according to claim 14, and further
comprising a delay timer connected between the integrator circuit
portion and the comparator circuit portion to thereby prevent or
reduce false signaling due to liquid sloshing.
16. An electrical circuit according to claim 15, wherein the
integrator circuit portion comprises a first resistor in series
with a capacitor and the delay timer comprises a second resistor in
parallel with the capacitor.
17. An optical transducer according to claim 14, and further
comprising a selector switch portion connected between the outputs
of the first and second comparators and the load switch portion for
selecting the output of only one of the comparators.
18. An optical transducer according to claim 14, and further
comprising an anti-hysteresis circuit portion connected to the
inputs and outputs of the comparators to prevent oscillation of the
load switch portion.
19. An optical transducer according to claim 10, wherein the light
source and the photosensor are positioned within the hollow
interior of the housing.
Description
BACKGROUND OF THE INVENTION
This invention relates to optical transducers, and more
particularly to optical transducers for detecting liquid level and
the like.
FIGS. 1A 1C schematically depict a prior art optical transducer 10
for determining liquid level in tanks, vessels or the like. As
shown, the transducer 10 includes an optical body 12 with a conical
tip 14 at one end thereof, and a light source 16 and photosensor 18
at an opposite end thereof. In the absence of liquid as shown in
FIG. 1A, light from the light source 16 is normally projected
through the optical body 12 where it is internally reflected at a
conical measuring surface 20 of the conical tip 14 and returns to
the photosensor 18, as represented by arrow 22. When the conical
tip 14 is submerged in liquid, as represented by dashed line 24 in
FIG. 1B, the light is refracted out of the conical tip 14 and into
the liquid (arrow 26). The amount of light at the photosensor 18 is
thus significantly diminished. The presence or absence of liquid on
the transducer 10, and thus the level of liquid in a tank, vessel
or the like can be ascertained.
However, it has been found that liquid level transducers of
above-described type can produce erroneous signals. As shown in
FIG. 1C, when the liquid 24 descends to a level below the
transducer 10, one or more liquid droplets 28 may form on the
conical measuring surface 20 due to the surface tension of the
liquid and the surface energy of the surface 20. Consequently,
light is refracted out of the conical tip 14 and into the
droplet(s) 28, as shown by arrow 26, to thereby give a false liquid
level indication. This phenomena can occur whether the transducer
10 is in the horizontal position as shown, or in the vertical
position.
In addition to the above, it has previously been difficult to
construct a compact optical transducer that is capable of operating
through a wide temperature range due to the relative proximity of
the light source and photosensor to the liquid being measured.
BRIEF SUMMARY OF THE INVENTION
According to one aspect of the invention, an electrical circuit is
provided for a liquid level transducer having a transparent body
that is adapted for exposure to a liquid to be measured. The
electrical circuit includes a light source adapted for projecting
radiant energy into the transparent body and a photosensor adapted
for detecting a level of the radiant energy emanating from the
transparent body. The level of radiant energy is indicative of the
presence or absence of liquid on the transparent body. The
electrical circuit also includes a pulsing circuit portion
connected to the light source for pulsing the light source between
on and off conditions, a rectifier circuit portion connected to the
photosensor for rectifying a signal from the photosensor, with the
rectified signal being proportional to the detected level of
radiant energy, an integrator circuit portion connected to the
rectifier circuit portion for temporarily storing the rectified
signal, a comparator circuit portion connected to the integrator
circuit portion for comparing the rectified signal with a
predetermined value, and a load switch portion connected to the
comparator circuit portion for switching an external load when the
rectified signal is at least one of above and below the
predetermined value.
According to a further aspect of the invention, an electrical
circuit is provided for a liquid level transducer having a
transparent body that is adapted for exposure to a liquid to be
measured. The electrical circuit includes a light source adapted
for projecting radiant energy into the transparent body and a
photosensor adapted for detecting a level of the radiant energy
emanating from the transparent body. The level of radiant energy is
indicative of the presence or absence of liquid on the transparent
body. The electrical circuit further includes a comparator circuit
portion connected to the photosensor for comparing the detected
level of radiant energy with a predetermined value. The comparator
circuit portion has first and second comparators, with the first
comparator being configured to output a high signal when the
detected level of radiant energy is above the predetermined value,
and the second comparator being configured to output a low signal
when the detected level of radiant energy is above the
predetermined value. A load switch portion is connected to an
output of at least one of the first and second comparators for
switching an external load when the detected level of radiant
energy is at least one of above and below the predetermined
value.
According to yet a further aspect of the invention, an optical
transducer for determining the presence or absence of liquid in a
reservoir comprises a housing with a hollow interior and an optical
probe that extends through the housing with a proximal end of the
optical probe being positioned in the hollow interior and a distal
end of the optical probe being positioned outside of the housing. A
light source is positioned for projecting radiant energy into the
optical probe toward the distal end. A photosensor is positioned
for detecting a level of radiant energy reflected from the distal
end, with the level of radiant energy being indicative of the
presence or absence of liquid on the optical probe. A comparator
circuit portion is connected to the photosensor for comparing the
detected level of radiant energy with a predetermined value. The
comparator circuit portion comprises first and second comparators,
with the first comparator being configured to output a high signal
when the detected level of radiant energy is above the
predetermined value, and the second comparator being configured to
output a low signal when the detected level of radiant energy is
above the predetermined value. A load switch portion is connected
to an output of at least one of the first and second comparators
for switching an external load when the detected level of radiant
energy is at least one of above and below the predetermined
value.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary as well as the following detailed description
of the preferred embodiments of the present invention will be best
understood when considered in conjunction with the accompanying
drawings, wherein like designations denote like elements throughout
the drawings, and wherein:
FIG. 1A is a schematic view of a prior art optical liquid level
transducer in a first operating condition;
FIG. 1B is a view similar to FIG. 1 of the prior art optical liquid
level transducer in a second operating condition;
FIG. 1C is a view similar to FIG. 1 of the prior art optical liquid
level transducer in a failure condition;
FIG. 2 is a side elevational view of an optical liquid level
transducer in accordance with the invention;
FIG. 3 is a top plan view of the optical liquid level transducer of
FIG. 2;
FIG. 4 is a sectional view of the optical liquid level transducer
taken along line 4--4 of FIG. 2;
FIG. 5 is a sectional view of the optical liquid level transducer
taken along line 5--5 of FIG. 4;
FIG. 6 is an end view of the optical liquid level transducer as
seen in the direction of line 6--6 of FIG. 4, in accordance with a
further embodiment of the invention; and
FIG. 7 is an electrical schematic in accordance with the present
invention that forms part of the liquid level transducer of FIG.
2.
It is noted that the drawings are intended to depict only typical
embodiments of the invention and therefore should not be considered
as limiting the scope thereof. It is further noted that the
drawings may not be necessarily to scale. The invention will now be
described in greater detail with reference to the accompanying
drawings.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings and to FIGS. 2 and 3 in particular, an
optical liquid level transducer 100 in accordance with the present
invention is illustrated. The optical transducer 100 preferably
includes a housing 102, an optical probe 104 extending from a
distal end 106 of the housing 102, and a wiring harness 108
extending from an opposite proximal end 110 of the housing.
With additional reference to FIGS. 4 and 5 6, the housing 102 is
preferably constructed of a metal material, such as brass. The
housing 102 includes a mounting section 112 with external threads
114 for engagement with internal threads 116 of a reservoir housing
118, which may be in the form of a tank, vessel, container or the
like. The housing 102 also preferably includes a securing section
120 with generally flat, external faces 122 for engagement by a
wrench or the like (not shown) for installing and removing the
optical liquid level transducer 100 with respect to the reservoir
housing 118 in a well-known manner. It will be understood that the
housing 102 can be constructed of other materials such as plastic
or ceramic. The particular configuration of the housing 102 will
largely depend on the mounting arrangement of the reservoir housing
118. Accordingly, the external threads 114 and external faces 122
may be eliminated and other mounting means may be provided. The
securing section 120 has a wall 126 with the external faces 122
formed thereon and a generally cylindrical interior cavity 124
delimited by an interior surface 128 of the wall.
In accordance with a further embodiment of the invention as shown
in FIG. 6, one or more of the external faces 122 may be provided
with cooling grooves 125 and/or fins 127 (FIG. 6) extending
generally parallel with a longitudinal axis 178 of the housing. The
grooves and/or fins increase the outer surface area of the housing
102 so that heat within the housing 102 can be more efficiently
transferred to the outside environment. In this manner, the
electronics and other components located within the housing may
have lower temperature requirements. It will be understood that the
grooves and/or fins have any orientation with respect to the
central axis 178.
An annular step 130 is formed in the interior surface 128 for
supporting a circuit board 132 within the cavity 124. An end cap
134 has an annular side wall portion 136 and a plate or disk
portion 138 connected to the side wall portion. The annular side
wall portion 136 is preferably in sealing engagement with the
interior surface 128 of the wall 126. An end 140 of the annular
side wall portion 136 opposite the disk portion 138 abuts the
circuit board 132 and holds it in place against the annular step
130. An annular flange 142 of the wall 126 can be pressed, rolled
or otherwise deformed over the plate portion 138 to hold the end
cap and circuit board in the interior cavity 124. It will be
understood that other means for holding the components together can
be employed, such as adhesive, welding, heat staking, and so
on.
Electrical wires 144 from the circuit board 132 exit the housing
102 through a central opening 146 formed in the plate portion 138.
A strain relief device 148 may be mounted in the opening 146 with
the wires 144 extending therethrough in a well known manner.
In accordance with a further embodiment of the invention, the
wires, strain relief device and/or end cap may be replaced with a
male or female plug portion with electrical connectors (not shown)
for mating with a female or male plug portion (not shown),
respectively, of the vehicle or system on which the liquid level
transducer 100 is to be installed.
The mounting section 112 has a central bore 150 that, before
installation of the optical probe 104, intersects the interior
cavity 124. The optical probe 104 extends through the central bore
140 and is preferably sealingly connected to the mounting section
112 at the distal end 106 of the housing 102 through an epoxy
adhesive layer 152 or the like to prevent liquid from entering the
bore 140 and interior cavity 124. It will be understood that other
means for connecting and/or sealing the optical probe to the
housing can be used, such as press-fitting the probe in the
housing, insert or injection molding the probe directly to the
housing, using one or more O-rings between the probe and housing,
ultrasonically welding the probe to the housing, using other types
of adhesives and sealants, and so on.
The optical probe 104 is preferably in the form of a transparent
body of generally elongate cylindrical shape with a proximal end
160 and a distal measurement end 162. However, it will be
understood that the optical probe 104 can have other cross
dimensional shapes, such as oval, square, triangular, and so
on.
It will be understood that the term "transparent" as used herein
refers to a material condition that ranges from optically clear to
opaque for various wavelengths of radiant energy. By way of
example, some materials that allow transmission of a substantial
amount of radiant energy in the visible light region of the
electromagnetic spectrum may not allow significant transmission of
radiant energy in the infrared or other regions. Accordingly, a
suitable transparent material would allow the transmission of a
measurable amount of radiant energy of a selected wave length
through the probe 104. By way of example, the probe 104 can be
constructed of glass material such as borosilicate or quartz;
Teflon.RTM. material such as PTFE, FEP, ETFE; plastic material such
as acrylic, nylon, polysulfone, polyetherimide, silicon,
polyurethane, polycarbonate, and so on. However, it will be
understood that the present invention is not limited to the
particular materials described.
The proximal end 160 of the optical probe 104 preferably abuts or
is at least closely adjacent to a light source 164 and photosensor
166 mounted on the circuit board 132.
The light source 164 is preferably of the LED type, and both the
light source and photosensor can be surface-mount devices with
recessed light emitting and light detecting areas 168 and 170,
respectively, to both efficiently couple the devices to the optical
probe 104 and prevent the direct transmission of stray light from
the light source to the photosensor. By way of example, a suitable
light source may be a high brightness surface-mount LED, such as
Vishay TLM 33 series or TSMS3700. Likewise, a suitable photosensor
may be a surface-mount phototransistor, such as Vishay
TEMT3700.
A suitable combination light source/photosensor pair 165 (shown in
dashed line in FIG. 7) may alternatively be used. One such
combination is a reflective object sensor, such as QRD1114 provided
by Fairchild Semiconductor. The reflective object sensor includes
an integrated infrared LED emitter 164 and phototransistor 166 in a
single package. Preferably, the measurement side of the reflective
object sensor abuts the proximal end 160 or is at least closely
adjacent thereto.
It will be understood that other light sources can be used, such
as, without limitation, incandescent bulbs, laser diodes, or any
other source that emits radiant energy in one or more of the
visible, ultra-violet, or infra-red spectrums. It will be further
understood that other photosensors can be used, such as, without
limitation, photocells, photodiodes, and photoconductors. In
accordance with yet a further embodiment of the invention, a single
integrated unit such as a proximity sensor having both the light
source and the photosensor may be used.
It will be further understood that the position of the light source
and photosensor may be reversed or located at other positions on
the proximal end 160 of the optical probe 104. In addition, the
light source and photosensor may be remotely located from the
proximal end of the optical probe and positioned for emitting light
into the optical probe and receiving light therefrom, respectively,
through intermediate members such as fiber optics, transparent
rods, or other suitable light guides.
The distal measurement end 162 of the optical probe 104 has a first
measurement surface 172 and a second measurement surface 174. The
first and second measurement surfaces intersect at a transverse
edge 176. Preferably, each measurement surface 172,174 forms an
acute angle A with respect to the central axis 178, as shown in
FIG. 3. In addition, the edge 176 preferably forms an acute angle B
with respect to the central axis 178, as shown in FIG. 2. The edge
176 together with the outer surface 180 of the probe form a pointed
probe apex or tip 182. Preferably, angles A and B are each
approximately 45 degrees. It will be understood, however, that
angles A and B can vary over a wide range depending on the type of
light source used and/or the liquid(s) to be measured. It will be
further understood that the probe tip 182 need not be pointed. In
addition, more than one edge 176 can be provided with more than two
intersecting measurement surfaces.
As best shown in FIGS. 4 and 5, with the optical probe 104
installed in the housing 102, an annular gap 184 is formed in the
interior cavity 124 between the housing 102 and the probe 104. The
annular gap 184 surrounds the probe 104 and serves as an insulative
barrier between the housing and proximal end 160 of the probe.
Accordingly, heat transfer between the wall 126 of the housing 102
and the probe 104 occurs by convection through the gap 184 rather
than by conduction to thereby limit the temperature of the proximal
end 160 of the probe. The temperature of the proximal end 160 can
also be controlled through heat conduction with the reservoir
housing 118. As shown in FIG. 4, the reservoir housing 118 may
serve as a heat sink to draw heat away from the optical probe 104
and the mounting section 112 through conductive heat transfer. If
desired, the annular gap 184 and/or a portion of the interior
cavity 124 below the circuit board 132 may be filled with
insulative material (not shown).
In the absence of liquid, as shown in FIG. 4, light entering the
optical probe 104 from the light source 164 is reflected off the
measurement surfaces 172,174 and back into the probe, as
represented by arrow 186, so that the photosensor 166 can detect at
least a portion of the light emitted by the light source 164. The
shape of the optical probe 104 encourages any liquid droplet(s) 188
(shown in phantom line in FIG. 2) that may initially be on the
measurement surfaces 172, 174 to be expelled from the optical probe
104. The relatively narrow areas at the edge 176 and tip 182
discourage the adhesion of droplets due to the relatively small
surface energy at these locations. Accordingly, the droplets will
tend to slide under gravity along the edge 176 toward the probe tip
182 where it is expelled from the optical probe 104. In this
manner, at least a substantial area of the measurement surfaces are
clear of the droplets, whether the probe is in the horizontal or
vertical position. Thus, any liquid that may otherwise remain on
the measurement surfaces is at least substantially reduced to
thereby give greater measurement reliability over prior art optical
liquid level detectors.
In order to further reduce the surface energy of the optical probe
104 and repel liquids, a low surface energy film such as Novec.TM.
provided by 3M or other fluorinated polymer or low surface energy
material, can be applied at least to the measurement faces 172, 174
of the probe, and preferably to the entire probe surface that will
be exposed to liquid. Another suitable film is a silicone hardcoat,
such as PHC587 provided by GE Silicones. The film should have a
lower index of refraction than the material of the probe 104 so
that in the absence of liquid, light from the light source 164 is
reflected back into the probe material. By way of example, an
optical probe 104 constructed of polysulfone has a refractive index
of approximately 1.63. A Novec.TM. film covering the polysulfone
probe has a refractive index of approximately 1.38, while a
silicone hardcoat has a refractive index of approximately 1.42.
With such an arrangement, it has been found that the voltage
differential of the probe between a dry condition and an immersed
condition in water is significantly enhanced. It will be understood
that a wide range of materials can be used for both the probe tip
and the film.
In the presence of liquid, the light from the light source will be
refracted out of the optical probe 104 to thereby create a signal
change that can be used to trigger a visual or audio indicator to
alert an operator that the liquid level in the reservoir 118 is at
a predetermined level. Alternatively, the abrupt signal change can
be used to automatically start and/or stop operation of a pump or
the like (not shown) to fill the reservoir with liquid to a
predetermined level.
Where it is desirous to continuously monitor the high and low level
of liquid in a reservoir for automatically filling the reservoir to
a predetermined level, two of the optical transducers 100 can be
used in conjunction with other circuitry to automatically start and
stop operation of a pump at the low level and high level,
respectively.
With reference now to FIG. 7, an electrical circuit 200 in
accordance with an exemplary embodiment of the invention for use
with the optical liquid level transducer 100 is illustrated. The
electrical circuit 200 preferably includes the reflective object
sensor 165 as previously described, which has an LED 164 that emits
infrared light and a phototransistor 166 that detects reflected
infrared light from the LED. It is understood, however, that other
light sources and/or photosensors can alternatively be used, as
previously described. A pulsing circuit portion 202 is connected
the LED 164 and a rectifier circuit portion 204 is in turn
connected to the photransistor output 206. An integrator circuit
portion 208 is connected to the output 210 of the rectifier circuit
portion and a delay timer 212 is connected to, and incorporates
part of, the integrator circuit portion 208. A comparator circuit
portion 214 is connected to the output 216 of the delay timer 212.
A selector switch portion 218 is connected to the comparator
circuit portion 212 and an anti-hysteresis circuit portion 220 is
connected to the output 222 of the selector switch portion 218 and
the output 216 of the delay timer 212. A load switch portion 224 is
also connected to the output 222 of the selector switch portion
216. Preferably, the load switch portion 224 is in the form of an
N-channel MOS FET. However, other switching means can be used, such
as power transistors, relays, and so on. A transient voltage
suppressor 226 may be provided in parallel with the load switch
portion 224 to protect the load switch portion against voltage
spikes.
The pulsing circuit portion 202 includes a pulse generator 228
connected to a regulated power supply 230, as well as resistors
232, 234 and capacitors 236, 238 for creating a square wave that
pulses the light source 164 between on and off states at a
predetermined frequency and duty cycle. The pulse generator 228 is
preferably in the form of a 555 timer IC, although other known
means for generating a pulse to the LED can be used. The particular
values of the resistors and capacitors determines the frequency and
duty cycle of the output pulse in a well-known manner. In
operation, the LED 164 is pulsed on and off at a predetermined
frequency and duty cycle by the pulse generator. The intensity of
the LED during the "on" state can be adjusted by varying the value
of a resistor 239 that is connected between the pulse generator 202
and the LED 164.
The rectifier circuit portion 204 includes a resistor 240 connected
between the photosensor output 206 and ground 242, a capacitor 244
having a first end connected to the phototransistor output 206 and
a second end connected between a pair of diodes 246, 248. When the
LED 164 is in the "on" state, the capacitor 244 will charge and
pass current to the integrator circuit portion 208 through the
diode 248. When the LED 164 is in the "off" state, the capacitor
244 will discharge to ground through the resistor 240. The diode
246 ensures that the discharge path will always be through the
resistor 240. Accordingly, any direct current (DC) offset that may
be present due to ambient light on the phototransistor 166, leakage
current of the phototransistor at elevated temperatures, as well as
other noise, can be reduced or eliminated. It is understood that
other means for reducing or eliminating noise may alternatively be
used.
The integrator circuit portion 208 includes a resistor 250
connected in series with the diode 248 and a capacitor 252
connected between the resistor 250 and ground, while the delay
timer 212 includes the capacitor 252 connected in parallel with a
resistor 254, which is in turn connected to ground. When the LED is
in the "on" state, current from the rectifier circuit portion 204
will pass through the resistor 250 and charge the capacitor 252 to
thereby hold or store the peak value of the pulsed signal, which
will also be present at the comparator circuit portion 214. When
the LED is in the "off" state, the capacitor 252 will discharge to
ground through the resistor 254. Preferably, the values of the
resistors 250, 254 and the capacitor 252 are chosen such that the
charge time of the resistor 250 and capacitor 252 is greater than
the discharge time of the resistor 254 and capacitor 252. In this
manner, an anti-sloshing feature is realized. When the liquid level
within the tank 118 (FIG. 4) or the like approaches a predetermined
level, any vibration or sloshing of the liquid may cause the
comparator circuit portion 214 and thus the load switch portion 224
to oscillate. With the above-described anti-sloshing feature, rapid
switching at the comparator output due to liquid vibration or
sloshing is greatly reduced. The particular duration of the time
delay can be adjusted by modifying the values of the resistors 250,
254 and the capacitor 252.
The comparator circuit portion 214 includes a first voltage
comparator 254, a second voltage comparator 256, and a voltage
divider 258 connected to the comparators. The comparators are
arranged such that the positive input of the first comparator 254
is connected to the output 216 of the integrator circuit portion
208 and the negative input of the second comparator 256. Likewise,
the negative input of the first comparator 254 is connected to the
positive input of the second comparator. In this manner, when the
output 264 of the first comparator is high, the output 266 of the
second comparator 256 will be low, and vise-versa.
The voltage divider 258 includes a first resistor 260 connected to
the regulated power supply 230 and a second resistor 262 connected
between the first resistor 260 and ground. A voltage divider output
268 is connected between the resistors 260, 262 and extends to the
negative input of the first comparator 254 and the positive input
of the second comparator 256.
In use, the integrated signal present at the output of the
integrator circuit portion is compared to a predetermined voltage
signal as defined by the voltage divider 258. When the integrated
signal is higher than the predetermined signal, the output 264 of
the first comparator 254 will be high and the output 266 of the
second comparator will be low. Likewise, when the integrated signal
is lower than the predetermined signal, the output 264 of the first
comparator 254 will be low and the output 266 of the second
comparator will be high. Adjustment of the predetermined voltage
signal can be accomplished by adjusting the values of one or more
of the resistors 260, 262. It is understood that one or both
resistors may be replaced with one or more potentiometers to
thereby provide a manually adjustable threshold setting.
The selector switch portion 218 includes a first switch segment 270
connected to the output 264 of the first comparator 254 and a
second switch segment 272 connected to the output 266 of the second
comparator. As shown, when the first switch segment 270 is in a
closed position, the second switch segment 272 is open. Likewise,
when the first switch segment 270 is open (shown in dashed line),
the second switch segment 272 is closed (shown in dashed line). In
this manner, the output from only one of the voltage comparators
will be connected to the output 222 of the selector switch portion
218. This feature is especially advantageous since a single circuit
board can be manufactured for two different modes of operation and
selectively switched to the desired mode. In the first mode, the
load switch portion 224 is closed when the optical probe 104 (FIG.
4) of the optical transducer 10 is dry, and open when the optical
probe 104 is immersed in liquid. In the second mode, the load
switch portion 224 is open when the optical probe 104 is dry, and
closed when the optical probe 104 is immersed in liquid.
By way of example, depending on the position of the optical probe
104 within a tank 118 or the like, the first operational mode can
be used to stop operation of a pump, relay, or other load 280 (as
represented by dashed line in FIG. 7) and/or to inform an observer
that liquid in the tank has descended below a predetermined level
through a visual and/or audio indicator, or other load 280 when
liquid in the tank reaches a predetermined level. Likewise, the
second mode of operation can be used to start operation of a pump,
relay or other load 280 when liquid in the tank descends below a
predetermined level and/or to inform an observer that the liquid in
the tank has risen above a predetermined level.
The first and second switch segments are preferably in the form of
jumper wires that are directly soldered to the circuit board during
manufacture. One of the wires can then be cut so that only one mode
of operation is available. It is understood that other means for
switching between the two operational modes can be used, such as
one or more manually selectable switches, jumper pins, traces that
can be cut during manufacture, a zero or low Ohm resistor placed at
either the first or second switch segment position, and so on.
The anti-hysteresis circuit portion 220 includes a first resistor
282 connected to the output 222 of the selector switch portion 218,
a second resistor 284 connected between the first resistor 282 and
ground, and a third resistor 286 having one end connected between
the first and second resistors 282, 284 and another end connected
to the positive input of the first comparator 254 and the negative
input of the second comparator 256. Preferably, the values of the
resistors 282, 284 and 286 are selected such that once the selected
comparator switches states, i.e. from a high state to a low state
or vice-versa, a predetermined offset voltage is added to the
appropriate input of the selected comparator to thereby prevent
oscillation at the switch threshold. Accordingly, oscillation of
the load switch portion 224 is prevented.
It will be appreciated by those skilled in the art that changes
could be made to the embodiments described above without departing
from the broad inventive concept thereof. Although the present
invention has been described in conjunction with detecting the
presence or absence of a liquid, it will be understood that the
term "liquid" can refer to any material (whether fluent or solid)
that, when in contact with the optical probe, causes a measurable
change in light intensity as detected by the photosensor. It will
be understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
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